Cambridge International Mathematics

218 Topics in arithmetic (Chapter 10)

EXERCISE 10D

1 Linda scored80%in her French test. If she received 60 marks, find the total number of marks possible

for the test.

2 45%of the students at a school are boys. If there are 279 boys, how many students are at the school?

3 The legs account for40%of the total weight of a table. If the legs weigh 16 kg, find the total weight

of the table.

4 A walker has travelled 9 km along a trail. If he has completed80%of the trail, how much further does

he still have to go?

5 Heidi pays22%of her monthly income in tax, and spends5%on petrol. If Heidi pays$ 1034 each

month in tax, find:

a her monthly income b the amount she spends on petrol each month.

6

7 On a hot day a metal rod expands by 1 :25%to become 1 : 263 m long. What was its original length?

8 Twenty years ago, Maria invested a sum of money. It has increased by119%to reach a value of$1095.

What was her original investment?

9 A car is sold forE 7560 at a loss of10%. What was the original cost of the car?

In Susan’s Casualwear business she buys items at a certain price and has to increase this price by40%to

make a profit and pay tax.

Suppose she buys a pair of slacks for$80. At what price should she mark them for sale?

One method is to find40%of$80and add this on to$80,

40%of$80 = 10040 £$80 = $32

So, the marked price would be $80 + $32 = $112.

This method needstwo steps.

Aone-stepmethod is to use amultiplier.

Increasing by40%is the same as multiplying by 100% + 40% or 140%.

So, $80£140% = $80£ 1 :4 = $112

Example 13 Self Tutor

What multiplier corresponds to:

a a25%increase b a15%decrease?

a 100% + 25% = 125% ) multiplier is 1 : 25

b 100%¡15% = 85% ) multiplier is 0 : 85

E MULTIPLIERS AND CHAIN PERCENTAGE [1.8]

Aisa

method for

increasing or

decreasing quantities.

multiplier

one-step

The population of a city has increased by8%over the last 10 years to151 200. What was the population

10 years ago?

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Y:\HAESE\IGCSE01\IG01_10\218IGCSE01_10.CDR Thursday, 2 October 2008 12:10:15 PM PETER